1. Field of the Invention
The present invention relates to a filter adapter configured to be detachably mounted on a camera body of, for example, a digital camera in a state that the filter adapter is externally fitted on a zoom lens barrel. The filter adapter is detachably provided with an optical filter on an end portion of the filter adapter at an object side.
2. Description of the Related Art
In a single-lens reflex camera, an inner circumferential portion of a top end portion of a zoom lens barrel is provided with a female screw portion formed thereon and an optical filter is screwed onto the female screw portion in a detachable manner.
Japanese Patent Application Laid-open No. 2007-212971 discusses an adapter ring detachably mounted on a camera body in a state that the adapter ring is externally fitted on the zoom lens barrel and a technique that an optical filter is detachably mounted on a top end portion of the adapter ring.
The adapter ring includes a mask for preventing an inner reflection inside a protection tube such that the mask is movable in an optical axis direction. The mask is pressed in a direction in which the mask contacts a top end portion of a lens barrel (i.e., toward the camera body) by a coil spring. When the lens barrel is extended to a photographing position, the top end portion of the lens barrel contacts the mask and, in this state, the lens barrel moves in an optical axis direction toward an object side against the pressure force of the coil spring.
However, in a case where an optical filter is screwed onto a female screw portion formed on the inner circumferential portion of the top end portion of a zoom lens barrel of a single-lens reflex camera, if the optimum filter diameter that does not block a photographing optical path is set, only the top end portion of the lens barrel has a large diameter, so that the lens barrel itself becomes large in size.
On the other hand, in Japanese Patent Application Laid-open No. 2007-212971, the lens barrel itself can be prevented from becoming large in size since the optical filter is mounted on the top end portion of the adapter ring, which is externally fitted on the lens barrel. However, in Japanese Patent Application Laid-open No. 2007-212971, since a protection tube is externally fitted over the entire range of the lens barrel in a state that the lens barrel is most extended (i.e., in a telephoto state), a length in the optical axis direction becomes longer when the adapter ring is mounted on the camera body. The length in the optical axis direction does not change even when the lens barrel is retracted, so that there is an issue in portability of the camera.